Multiple catastrophic failures of aftermarket crossmember kits have motivated a recent evaluation of the safety of these units.

Additionally, general concerns about the viability of Mustang II suspensions in home-built hot rods have come to the forefront.

Some rod builders are insisting on only purchasing certain types of units, from certain manufacturers, with specific modifications. Others are opting for installing a stock Mustang II crossmember for safety purposes, choosing to rely on Detroit engineering over aftermarket manufacturers.

Here are some of the questions that have been raised on the Hotrodders Bulletin Board in regards to Mustang II crossmembers:

"It doesn't matter who builds your chassis, a pro-builder or if you do it at home, when components are "adapted" it can put a different type of stress on parts that may have not been tested by the factory for that particular type of stress. Street rod chassis manufacturers and parts manufacturers don't have the facilities or money to test their units for structural integrity the way Detroit does so regular inspections are a must." (Centerline)

"You have to pay attention to detail when buying one of them, and even more when installing one." (Primemover)

"Another example is the broken Heidt's x-members that have been publicized here recently. That design is flawed since it introduces a stress riser at a highly stressed point in the x-member then eliminates the strut rods which were intended to lessen the stress in that location. Give that design to any graduate mechanical engineer and he will confirm that fatigue cracks are guaranteed." (willys36)

"In the cases of the very small minority who have had failures, these failures were most often the result of poor installation and/or using strut rod eliminator kits without proper strengthening of the crossmember." (Centerline)

"Being a mechanical engineer I have often wondered when something like this would happen. As many of you have observed there may be a problem with the fabricated front crossmember...not just this particular manufacturer but all in general, since they are all similar." (bentwings)

"I hate to say it but [Heidt's] design seems flawed to me, have a look under your factory vehicle and notice the design of the crossmember, I see none of those design features incorporated in this example." (4 Jaw Chuck)

"As far as testing our products, we introduced our Superide Independent Rear Suspension kits recently. I installed the first one in my '57 Chevy pick-up. It was a great opportunity to test a new product, as we left the box off the truck for two weeks so we could do torque and force measurements easily. I pounded on it as much as I could for those two weeks, literally driving through every pot hole and railroad track I could find. This kind of testing was great, as it showed that the design was sound." (Gary Heidt)

***On the statistical significance of crossmember failures:

"Five complete structural failures in 40,000 for a critical suspension component would mean a massive recall to a manufacturer like one of the big three. I think his product was never tested to failure if you ask me and he is terrified of that coming out in a court room." (4 Jaw Chuck)

"An estimate of all the manufacturers in entire street rod industry would show that there were probably a total of 30,000 sets of control arms and 40,000 crossmembers sold in the last 10 years combined. Of all these products out there from all these companies, don't you think that if there was a genuine problem with this type of design that there would be hundreds and hundreds of failures, not just a hand full?" (Gary Heidt)

"It sounds like Fatman has one heck of a sales crew and know just what to say, but 5 failures in 40,000 units is a VERY high number, that means that you have a 1:8,000 chance of a catastrophic suspension failure (if that was the standard new cars were made to 20,000 new cars would have a front suspension failure every year in the United Sates alone!!)" (deuce_454)

To view the entire discussions from which these quotes were taken, visit the links below:

Jon this is a great idea to spur a constructive dialog on the safety of these systems. What we will have to be careful of is the tendency to "bash" a particular brand from a user stand point and the manufacturers are going to have to stand back and do their best not to get too defensive when people voice concerns.

I don't believe there is a single company out there that would intentionally produce a flawed product, especially when it comes to the safety of their customers. If there are insights the manufacturers may have on problem areas the shade-tree mechanic should be aware of it would certainly be beneficial to everyone.

One thing this should not be is one of those "my product is better than the other guys" arguments.

I am in agreement with Centerline in that maybe this forum could in the long run be used to improve the units that many of us now have under our cars. I have been on the NSRA Kansas safety team for 3 years and have seen some things that were so unsafe I told the owner that he should put it on the trailer to take it home. One thing I found on my own car this year is that when I installed the sway bar the links were too short (less than 1/2 inch clearance) and would some times make contact with the inner tie rod ends on the MII rack when I would hit a bump in the road, mostly at slow speeds, installed a slightly longer link and the problem was solved. Most of the things that I have seen were installation problems although a couple of my fellow inspectors found a unit in a car that was made out of much too thin of metal. On a related subject I have seen brake lines mounted with wire ties and just about every manner and the same car running without an e-brake, that is a disaster just waiting to happen. One last thing if you are at a show and they are doing safety inspections do yourself a favor and let these guys and gals have a look at your car, they are all volunteers and are not there to criticize you ride they just give you a second set of eyes that may see something that you missed, it does happen. Well I have put in my 2 cents worth so need to let someone else have the soapbox.:thumbup:

poncho62

10-14-2003 06:42 PM

I put a Nova subframe in my 51 Ford pickup. Frame and all. Made sure it was absolutely square. Look at it this way.....GM spends millions on designing these suspension systems. Why let some little fly by night manufacturer come between "your" LIFE AND DEATH.

Tony@AirRideTech

10-15-2003 09:47 AM

I know almoast all of the front crossmember manufacturers personally and I can surely tell you guys that there is no way ANY of them would pass off a product to the public if they even had the smallest idea of it being a flawed design. Now true there are a few "less desireable" designs and some front ends that should only be used on very light smaller street rods, there is one thing we need to keep from doing here and that is pointing a finger without knowing all of the CORRECT information. A failure such as a few mentioned in the previous posts could have been caused by a number of different factors. The largest factor in my opinion, besides the obvious faulty install is the condition of the original frame and chassis. If the original chassis is worn out and exhibits an abnormal amount of flex its a no brainer that there will eventually be a premature failure.
Personally, I would use an aftermarket crossmember long before I went to a bone yard to cut out an OEM piece...... My point in all of this is that we do not need to jump on the fingerpointing bandwagon until all of the votes are in. We also have to keep in mind that for the most part we are dealing with Hot Rods that have had decades of modifications performed to them and we are also dealing with manmade components that require a great deal of expertise to install properly. :)

farna

10-16-2003 03:16 PM

Tony has a good point. Hot rod suspensions really aren't designed to be pounded constantly like an OEM system. Many were designed for light cars and are being installed in daily driven cars. But on the same token we KNOW where the weak points are now. I don't expect small manufacturers (relative to the big auto manufacturers) to test designs as much as the OEMs, but there should be improvements made now that we know where the weak points are. There should be extra braces and warnings sent with strut rod eliminators as well -- that seems to be the crux of the problem. I haven't seen an aftermarket MII crossmember failure when used with strut rods, just when the strut rod eliminators are used. The only strut rod eliminator I've seen that looks safe doesn't mount to the crossmember -- it bolts in place of the strut rod and goes back near the same lines with a bracket that welds to the body. That type doesn't put added stress on the crossmember. The "A" arm types do.

Jon

10-16-2003 03:34 PM

What sent up a red flag for me was Heidt's response letter, in this thread. It's full of PR doubletalk, and comes across as an attempt to do some damage control. The way he's presenting the statistics on the number of failures leaves much to be desired.

I spoke with Fatman Fabrications on the phone at length. I was polite and diplomatic. They were cagey, rude, and defensive. If they're willing to discuss it, then I feel that they should have responded to my email and phone requests to address the issue in a public forum.

Tony -- maybe you can put in a good word for us with some of these MII manufacturers, or drop them a line and invite them to join in the discussion?

Pony

10-16-2003 05:26 PM

Years ago, when first introduced, the MII from end was only available for pre 34 rods. If you look at the size and weight of a MII vs. Early rods, they are fairly even. Other than poor installation I don't remember this issue ever coming up. Now the MII is available for just about everything. The MII was never designed or engineered for that kind of weight and stress and that now we have failures. Just look at what the front end was on: Pinto's and Mustang II's, hardly a Hi-Po front end design no matter how many coil-over shocks, ect, you throw at it. :)

Centerline

10-17-2003 07:16 AM

Quote:

Originally posted by Pony The MII was never designed or engineered for that kind of weight and stress and that now we have failures. Just look at what the front end was on: Pinto's and Mustang II's, hardly a Hi-Po front end design no matter how many coil-over shocks, etc, you throw at it. :)

Not true. I've heard this argument over and over again and it is based on a lack of understanding of how the Mustang II IFS was designed. People think Pinto and Capri (both light weight cars) but fail to remember that many Mustang II's (Cobra and Mach I) came equipped with the 302 and 4 speed.

A Mustang II equipped with a 302 loaded down with air conditioning put much more stress on the front suspension than most street rods would ever think of. What most people fail to understand is that this IFS was designed to have the engine mounted directly over the crossmember. When it comes to street rods, most typically mount the engine with the front crank dampener at the crossmember. This lowers the percentage of weight the front suspension has to support dramatically. That's why most cars running big blocks or Hemis only need 4 cyl. springs when using a Mustang II IFS. Because the engine is mounted further to the rear, the center of gravity (fore and aft) is moved rearward a significant amount and the front suspension simply doesn't need to support as much weight as it was originally designed to carry.

I know Jon didn't like Gary Heidts letter but Gary was correct. There are literally thousands of these systems (manufactured by many companies) on the road today. When you take into consideration the majority were installed by shadetree mechanics and the fact that some people insist on modifying Ford's original design by eliminating the strut rods, its a miracle there haven't been more failures. Of all the traversing of the internet I've done I have only read discussions of three people who experienced failures. Two were the result of using strut rod eliminators and one was a strut rod bracket that broke off the frame under braking due to poor bracing/welding.

When a Mustang II IFS system is installed properly, using stock Mustang components, including strut rods, they are very safe for all but the heaviest of street rods.

The most important factor in this whole equasion is "Who is welding what to what"..............:thumbup:

Quote:

Originally posted by Jon What sent up a red flag for me was Heidt's response letter, in this thread. It's full of PR doubletalk, and comes across as an attempt to do some damage control. The way he's presenting the statistics on the number of failures leaves much to be desired.

I spoke with Fatman Fabrications on the phone at length. I was polite and diplomatic. They were cagey, rude, and defensive. If they're willing to discuss it, then I feel that they should have responded to my email and phone requests to address the issue in a public forum.

Tony -- maybe you can put in a good word for us with some of these MII manufacturers, or drop them a line and invite them to join in the discussion?

Jon,
I hear what you are saying and to a point I will agree with you but I would also side with them for not coming into a discussion over an internet chat board. You could basically be inviting them to a hangmans party. With the number of shady internet users out there a conversation on a chat board can be very one sided.

EBlack36

10-17-2003 10:28 AM

I agree with both centerline and tony@airride in that it depends on where the engine is mounted on how much weight is placed on the front cross member. In the 36 the entire engine is behind the cross member and when I weighed the car after I got it completed in 97 the amount of weight on the front was within 25 pounds of the amount of weight on a V6 Mustang II. As I am not a professional welder I make sure and get my car up on a lift a couple of times a year just to make sure the I do not have any cracks. FYI i am running a stock MII cross member as no one was building a unit for the Pontiac when I started building the car in 1987. I have driven the car from Kentucky to Colorado and from South Dakota to Texas during that time and Have not had a single problem. I also have the strut rod eliminators and have not had a problem with them either. One of the problems that I have noticed on other cars is that some people try to get them very low and the lower arms are not setting level, this causes undo stress on all of the other suspension components, plus it makes them much more difficult to be aligned properly. My car aligns to stock 1976 MII specifications and I have never had a problem in getting it aligned. I have now used up a whole dime worth of time so I will get down off of the soap box for now.:thumbup:

bad_co_nova

10-17-2003 10:48 AM

I just recently installed a mustang II front end on my 63 nova and I haven't had any problems with it YET. I believe it is a safe and a well put together kit, from HEIDTS hotrod shop!

farna

10-17-2003 11:03 AM

EBlack36, what type strut rod eliminators are you using? Did you weld in any additional supports when the eliminators were installed?

As far as weight goes, Ford's not the first to use that type suspension. If you've ever seen a 64 or later Rambler or AMC, you'll see the same thing. AMC started using a strut rod (compressed, as with the MII) in 1962. The lower arm with ball joint and crossmember is very similar to the MII unit. The only significant difference is the location of the spring -- it's above the steering knuckle on the AMC design, similar to an early Mustang/Falcon. AMC used a big, heavy 287 and 327 V-8 at the time, about the size and weight of a 396 Chevy or 352/390 Ford engine. Only spring location is different in the small Fords too -- Falcon and Mustang used a similar setup. I think the Fairlane did too, but had front strut rods (in tension) rather than rear (in compression). So the overall design isn't flawed -- it's been used for years in different variations.

EBlack36

10-17-2003 11:11 AM

The ones that I am using are from a company in Colorado that I have the name in my tool box in the garage (I am at work right now) It came with a spacer and a gusset that I made sure was welded solid to the cross-member. and it bolts also to the lower control arm forming a complete A arm. The side effect is that it gave the car a better ride than it had with the strut rods.

Bluepen

10-17-2003 12:43 PM

Something I noticed

Heres something I noticed and I guess self corrected on my M II kit. I was short one bolt for the lower shock, the one bolt I had was a grade 8 and I asked on this board if it would be alright to use a grade 5 instead. Members told me no to use a grade 8 and that all the bolts should be grade 8. I checked and found that other bolts in the kit were grade 5, I can't remember now where they all went, but I replaced all bolts to grade 8. Is this something we should all look at??